Ordovician Hydrocarbon Accumulation and Main Controlling Factors in the Western Margin of Tazhong No.1 Slope-break Zone, Tarim Basin

The Tazhong low uplift is one of the areas which are abundant in oil and gas resources in the Tarim Basin, and oil and gas shows of different levels have been also found in the margin of the Tazhong No.1 slope-break zone, which has got high commercial hydrocarbon flow within the Lianglitage Formation in the Upper Ordovician, and low commercial hydrocarbon flow within the Yingshan Formation in the Lower Ordovician. Ordovician hydrocarbon accumulation process of TZ86—TZ45 area in the margin of the Tazhong No.1 slope-break zone was discussed through source rock correlation, oil and gas property, formation water property, inclusion homogenization temperature, et al. It is considered that there are three hydrocarbon filling periods for Ordovician, that is Late Caledonian, Late Hercynian and Yanshanian—Himalayan epoch. Oil and gas are from Cambrian—Lower Ordovician source rocks in the Late Caledonian period, and Middle—Upper Ordovician source rocks in Late Hercynian period. Both periods of oil and gas are from the direction of the TZ88 well through carbonate reservoir; Hydrocarbons for Yanshanian—Himalayan epoch are mainly natural gas which is of complex origin. In addition, the main controlling factors for this hydrocarbon-enriched area include multiple hydrocarbon source rocks and hydrocarbon filling periods, high quality carbonate karst reservoirs and the coupling relationship among reservoir-forming factors.